Designed as a smaller, short-ranged alternative to the Boeing 707 and 727, the 737 was first flown on April 9th, 1967. Over its long operational carreer, the 737 has spawned numerous variants ranging in capacity from less than 100 to more than 200 seats. In fact, the 737 series is the best-selling jetliner in aviation history with more than 6,500 aircraft manufactured to date and more than 4,500 still in service with over 500 airlines around the world. Incredibly, there is a 737 taking off or landing somewhere in the world, on average, every five seconds.